In a WRAN system of which a standardization process has been performed, a wireless Internet service is provided by using unused time and spaces of a primary user of television or wireless devices in a television frequency band or a wireless microphone communication frequency band, e.g., 54 MHz to 698 MHz band in channels ‘2’ to ‘51’ in case of USA, and 41 MHz to 910 MHz band in case of an international use.
The WRAN system provides an asymmetric digital subscriber line (ADSL) or a wideband Internet service similar to a cable modem to a home and an office, and has a typical service range having a cell radius of 33 km. Accordingly, a customer premises equipment (CPE) is fixed, and uses an adaptive modulation and an adaptive channel coding method to improve a packet throughput under an environment including cells having a large service range of a cell radius of 33 km to 100 km. A diversity using a repeated transmission of sub-carriers in OFDMA method is applied to satisfy a quality of service (QoS) at cell borders.
The WRAN system is included in technologies of which a standardization process has been performed in institute of electrical and electronics engineers (IEEE) 802.22. The current standardization process of IEEE802.22 is actively performed so that substitutes of standard regulations proposed from each country are integrated into a single standard regulation.
Meanwhile, adaptive modulation and adaptive channel coding technologies under a mobile wireless channel environment are previously proposed in an international mobile telecommunication-2000 (IMT-2000), a WLAN, and IEEE802.16. Main characteristics of the proposed technologies are to maintain a received signal quality and maximize a throughput in a limited channel resource by applying the adaptive modulation and adaptive channel coding scheme adaptively according to the receiving signal quality.
In an OFDMA method of the IEEE802.16 which is introduced as a conventional technology, each terminal assigns channels by clustered sub-carrier basis. The terminal applies the adaptive modulation and adaptive channel coding to different clustered sub-carriers on the same frequency channel.
However, in the OFDMA method, the PAPR increases by a modulation scheme and the number of sub-carriers of a high spectrum-efficiency. In modulation schemes of a binary phase shift keying (BPSK), a quadrature phase shift keying (QPSK), 16-quadrature amplitude modulation (16-QAM), 64-quadrature amplitude modulation (64-QAM) and 256-quadrature amplitude modulation (256-QAM), the BPSK scheme has the smallest PAPR value, and the 256QAM scheme has the largest PAPR value.
However, in the OFDMA method, the subscriber channels are assigned by the clustered sub-carrier basis. There is a problem that overall PAPR are determined by a modulation scheme having the largest PAPR value in case that a different modulation scheme is used in each subscriber channel.
Moreover, a cell radius of the WRAN system is about 33 km and has a large service range. However, in the OFDMA method, there is a problem that it is difficult to perform a ranging and a power control in a large service range.